Basements and BAS

I frequently find that if I include basement area and volume in a BPI calculation for Building Airflow Standard then relatively high flow rates will be considered too tight.

As I have gone through these projects these past 10 years, I have been ignoring basement area and volume when I calculate BAS, no matter how much the basement is used. I really think when they set up that calculation they did not anticipate anyone building with a basement. It also is logical that the basement would be ignored because you will not get a lot of infiltration from below grade walls.

The anecdotal answer whenever I ask this is ‘where is the insulation’? but that is a ridiculous proposition because insulation in a basement is not likely to influence infiltration in the house.

Insulation in a rim joist may influence infiltration, but if you are retrofitting a house with an unconditioned basement, and rim joist insulation and airsealing is part of the plan, you do not necessarily include basement area or volume when you calculate your ventilation requirements. Why would that change if the basement is conditioned? By airsealing the rim joist in the unconditioned space you influence the performance of the conditioned space but you have ignored the volume of the basmeent in your BAS calculation. Why would that logic change if the basement is conditioned? You still have the same number of occupants, appliances, and location of those appliances.

This determination is important because if you include basement volume, you may walk away from a job that really needs work because the calculations say the building is ‘too tight’.

These discussions will become much more murky when walkout basements are considered. Half the volume anyone?

Replies to This Discussion

I used AirAdvice. You leave it in the home for 3 days to a week and it logs Temp, RH, Radon, CO2, CO, VOC's, Allergens, etc...

Like many of the things I've done in this grand experiment, I did not get paid for the work. So I don't have a huge scientific statistical database to back up my observations. All this talk about IAQ made me curious, and I had access to the tool. It's simply another example of where measuring showed results leading in a direction I wasn't expecting. I now believe that "when you assume instead of measuring, your conclusions are likely to be embarrassingly incorrect."

I think soon we'll have inexpensive devices that track these things over time. Ecobee is pretty close:

What is the charge? What do you think it costs you to drop it off, pick it up, and deal with it? What percentage of houses would consider reasonable to measure? Have you then ventilated more and measured? Has anybody?

You can invest in a bunch of AirAdvice and let us know. They are not cheap devices, and I don't know anyone that has them that actively promotes the service. What would you need to hire someone to drive 30+/- minutes, install, then return and collect such a device, probably after business hours when people will be at home.

Then what, schedule a 3rd visit to review the results? (And this doesn't factor in sales and marketing costs) What do you need, $400? Tough way to make a living, quick way to go broke...

And then he problem I see is it's still just taking a small snapshot.

I don't want a week in October or July, I want the whole year. That's where patterns, and ability to see impact of results to changes to ventilation. That's where you can set "alarms" that e-mail or text you when air in your home goes out of spec.

On venting no matter what, when does venting become excessive air infiltration? Initial versions of Rem Rate ended up penalizing the score quite a bit due to energy use of the HRV. In the case of a ranch house, including the basment doubles the volume, which doubles the minimum ventialtion rate. Is that reasonable?

I have seen stuff here about different directives BPI, ASHRAE, saying include the basement regardless, but i do not hear any logical rational explanation of why. I do not understand how simply adding volume will increase the need for ventilation, yet the calcualitons offered all use volume as a variable to determine the need for venting. I wonder if the authors of those directives felt basement were outside the envelope or inconsequential and when they wrote ther standards the academics misinterperted the intent.

How is a slab on grade ranch with 4 occupants and gas fired appliances to serve that space different from the same house on an unconditioned basement? Why does basement volume matter if attic volume does not? We have not added any appliances, people, or other parameters that infliuence contaminants, we just added volume.

The personal habits of the occupants are a completely different argument and have variables none of us can predict. But, if you are at the hosue doing anassessment you should be able to see the way they use the house and at least ask about habits that may be imprudent or will require special ventilation.

I would argue the presence of a pet ferret will affect the need for ventilation more than the addition of a basement.

Someone on this discussion already said basement walls, especially block walls are pourous and actually allow significant infiltration unless they are addressed in a job scope. If we change the basement envelope I would agree we must include the basement volume in our calculations for required ventialtion. That is no different than adding any room. But if the scope does not address the basement I do not see the need to include the basemnt volume in the calculation.

I am still waiting for Joe Fitz or John Proctor, who probably wrote these directives, to chime in on their intent and reasoning.